NBS

PUBLICATIONS

A11107 es^a

NBS SPECIAL PUBLICATION 664

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

Gasification of

Refuse Derived Fuel

in a Paired Fluidized

Bed Pyrolysis Unit

100

.U57

No . 664

1933

c. 2
NATIONAL BUREAU OF STANDARDS

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OX rtAMDAJUM

Ocfoo

Gasification of Refuse Derived Fuel

in a Paired Fluidized Bed Pyrolysis Unit mj

S. Suzuki 1 and H. Yakowitz2

(1) Agency of Industrial Science and Technology

Japanese Ministry of International Trade and Industry

(2) Office of Recycled Materials

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued September 1983
Library of Congress Catalog Card Number: 83-600583

National Bureau of Standards Special Publication 664

Natl. Bur. Stand. (U.S.), Spec. Publ. 664, 45 pages (Sept. 1983)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1983

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $3.75

(Add 25 percent for other than U.S. mailing)
GASIFICATION OF REFUSE DERIVED FUEL IN A

PAIRED FLUIDIZED BED PYROLYSIS UNIT

Results developed as part of the scientific exchange

program of the respective governments of Japan and the United States

Prepared cooperatively by the Agency of Industrial Science and Technology,

Ministry of International Trade and Industry, Government of Japan,

Ebara Corporation, Japan (acting for the Government of Japan),

and the National Bureau of Standards

Text prepared under the direction of Mr. S. Suzuki (AIST)

Text edited by Dr. Harvey Yakowitz (NBS)

1
Foreword

As part of the scientific interchange program initiated by the

United States Government and the Government of Japan, the Department

of Commerce was selected by the White House to be the pilot agency

for a project concerned with resource recovery from discards

originally destined for waste. Such discards include municipal

waste and industrial waste. Under terms of the agreement signed by

the President and the Prime Minister on May 2, 1980, the United

States and Japan will exchange small teams of government scientists

in order to examine resource recovery in the respective countries

and to formulate possible joint research ventures.

The Office of Recycled Materials of the National Bureau of

Standards (NBS/ORM), which was charged with fulfilling the duties

assigned to the Secretary of Commerce by Subtitle E of the Resource

Conservation and Recovery Act as ammended (P.L. 94-580; PL 96-482) was designated as the U.S. contact point for this project. The

Japanese team visited the U.S. in December, 1981; NBS/ORM arranged

the itinerary and provided technical briefings and an overview of

resource recovery activities. At that time, NBS/ORM and Japanese

representatives concluded an agreement for joint research to be

performed as part of the project. The text is as follows:

AGREEMENT FOR JOINT RESEARCH JAPAN-UNITED STATES

Both sides agree to pursue item (1) proposed by Japan and item

(2) proposed by U.S. to fullest extent possible:

(1) Gasification of Refuse Derived Fuel, RDF (Ebara Corporation)

AIST has been carrying out R&D involving dual fluidized bed

gasification of the organic (plastic rich) portion of municipal

refuse by operating a pilot plant at Yokohama, Kanagawa Prefecture,

since 1973. The entire task has been carried out by Ebara Corporation under contract. This research is scheduled to be completed by

the end of FY 1982 (March 31, 1982).

The U.S. is currently producing RDF from municipal refuse for

possible use as substitute or supplemental fuel. If RDF could be

converted into high quality gas in an efficient and economical

manner, some beneficial application might be found, e.g., better

market opportunities for waste-to-energy applications. Additionally,

unwanted substances which are emitted by RDF in the course of its

incineration may possibly be eliminated by gasification of RDF. It

may be worthwhile to analyze the compositions of gas and other

substances produced by the pyrolysis.

The experiment can be carried out at the said pilot gasifier

in Yokohama. A specified amount (20 to 100 U.S. tons) of RDF will

be transmitted to Japan for this purpose upon request of Japanese

side. Data will be analyzed both in Japan and the U.S.

2
(2) Econometric models describing the market potential for various

forms of recycled materials and energy from waste have been developed

in the U.S. These models provide a basis for selecting the optimum

resource recovery strategy for a region in terms of:

o Markets available for the products

o Technology selection

o Size of plant

o Transportation network

o Refuse supply

o Costs and revenues over the lifetime of the project

The data required for carrying out this analysis include:

o Specifications for the products to be sold, e.g., heat

value, residues produced, pollution properties, quantity

produced per input ton of refuse

o Size of plant

o Efficiency of plant

o Requirement of plant for energy and other operating costs

o Requirement of plant for labor

o Capital cost of plant

o Lifetime of plant

o Required treatment, if any, of input refuse

o Type and amount of emissions and residues from plant

The U.S. undertakes to carry out market potential studies in

several areas of the United States for any and all sets of data

provided by Japan. Mutual benefits will be:

o Japan learns if the processes and products being produced

can be marketed in the U.S. profitably.

o Japan learns direction for further research to improve

processes and products in terms of marketability in the

U.S.

o U.S. learns whether Japanese technology can aid in dealing

with solid waste management problems in various regions

of the United States.

Both sides agree to further consider the attached lists of

possible research items for possible action at a later time.

3
PROPOSED BY JAPAN

Possible Joint Research Items

(Japanese Government Institutes)

1. Combustion Studies of RDF or Other Solid Fuels (Government

Industrial Development Laboratory, Hokkaido, AIST).

There is a 25 cm square fluidized bed combustion reactor now under test operation. Utilization of combustion heat by heat

exchange is studied here.

In response to the U.S. proposal (3) (see overleaf) physicochemical phenomena of combustion can be studied and some thermokinetic data may be obtained. RDF, coal, and other organic waste,

or their mixtures can be burned in the reactor and emissions such

as HC1, NH3 , CO, C0 2 , and hydrocarbons can be monitored.

2. Utilization of Ash Residues from an Incineration Plant

(National Chemistry Laboratory for Industry, AIST).

Treatment of ash residues from an incineration plant of

municipal refuse is an important issue from the viewpoint of

reducing the environmental burdens, and economically sound methods

to reuse such ashes need to be found. Research involves effective

classification of constituents in the ashes and utilization process

development on reclaimed substances as well as effective design of

the incineration system.

3. Acid Hydrolysis of Cellulose Materials

(The same Laboratory as 2. above.)

It is necessary to find the most economical process which

would convert waste or low cost biomass into ethanol. Enzymatic or acid hydrolysis process is first required to convert the cellulose

fraction of raw material into glucose.

A two-stage batch reactor of acid hydrolysis originally

designed is going to be examined.

4
PROPOSED BY UNITED STATES

Possible Joint Research Projects

1. Dusts created by the electric furnace process for the productionof steel contain valuable metal units . Economically sound

methods to recycle such dusts on furnace-by-furnace basis need

to be found. Research involves particle identification,

classification and design of a system to separate out desired

constituents.

2. Mill scales and sludges created by rolling processes in the

steel industry need to be doiled for reclamation of metal units . Research involves characterization of such wastes and means to

reclaim oils and/or energy plus metal units. Thermal and

chemical processes need to be compared.

3. Combustion products created by burning refuse or mixtures of

fossil fuels and refuse derived fuels need to be studied in

order to prevent unwanted emissions, e.g., dioxin, and to

provide for most efficient firing characteristics. Research

involves setting up on-line monitoring for unwanted emissions

and determination of basic thermokinetic data on the firing

process. For example, co-firing of coal with refuse derived

fuel reduces S0

x emissions drastically. The mechanism for

this process should be deduced in order to optimize use of

coal RDF mixtures for power boilers.

4. More economical means of recycling plastics from mixed wastes

are needed. The Japanese are ahead of U.S. on the technology

to do so. Joint research on new uses for waste plastics could

be beneficial to the U.S.

5. The corrosion propensities of refuse and various forms of

refuse derived fuels need to be studied. Joint research could

aid in assuring that the potential for downtime or even failure

of very expensive capital equipment is minimized.

Contact for Japan: S. Suzuki

AIST

Contact for U.S.: H. Yakowitz

NBS

NBS/ORM arranged to ship to Japan about 35 tons of fluff RDF

produced at the Baltimore County, MD resource recovery facility.

This material arrived in Japan in early November, 1982.

In accord with the foregoing agreement, this RDF was gasified

in a pilot scale resource recovery plant in Yokohama. The results

of this gasification experiment are described in this NBS Special

Publication. The text, as received from the Agency of Industrial

Science and Technology of the Japanese Ministry of International

Trade and Industry, was edited by Dr. Harvey Yakowitz, Chief,

NBS/ORM.

5
Special thanks are given to the Text-Editing Facility of the

National Measurement Laboratory of NBS for preparation of the final

version of the report.
Abstract

The refuse derived fuel (RDF) produced at the Baltimore County

Resource Recovery Plant and provided by NBS to the Government of

Japan was gasified in a paired-bed pyrolysis unit, i.e., a fluidizing

medium (sand) was circulated between a pyrolysis reactor and a combustion reactor. Thus, pyrolysis and combustion occur separate

from one another; hence, the name "paired-bed."

The gas refining equipment consists of two chains, one for

pyrolysis gas and the other combustion exhaust gas:

1. A cyclone separates char from the gas coming from the

pyrolysis py.no lygrs reactor. This char is fed to the

combustion reactor for burning. After the gas passes

through a heat exchanger and is quenched in a carbon

deposit protector, a tar-separator removes oil mist and

the gas is cleaned in a scrubber. A small portion of

this clean gas is pressurized by a blower, preheated in a heat exchanger and used to f 1 uidize the pyrolysis reactor

bed; the remaining gas is sent to a tank for storage.

2. The exhaust gas generated by the combustion reactor is

discharged into the atmosphere after being treated by

means of a two-stage cyclone and electric dust precipitator. The non-combustible substances contained in the

feed stock are discharged from the bottom of the combustion tower periodically.

The RDF was fed into the system at a rate of 0.6 to 1.0 tonnes

per hour. The pyrolysis reaction temperature was about 650 °C.' The

following ultimate analyses were performed: (N.B. "T" is "Trace")

1. Feedstock

a. Main components

C, H, N, CI, Na, K, Ca, Ash.

b. Harmful components

Cu, Pb, Cd, T-Hg, As, T-Cr, Al.

c. Heat value

2. Pyrolysis gas components

a. Main components

H

2 , 02 , N

2 , CH

4

, CO, C0

2

, CmHn.

b. Harmful gas components

HC1, H„S, NH„ , HCN, SO , NO . 2 4' ' x' x

c. Heat value

7
3. Flue gas

a. Main gas components

02 , N 2 , CO, C0 2

.

b. Harmful components

SO , NO , HC1, dust.

Ash

a. Main components

C, H, N, S, CI, Na, K, Ca.

b. Heavy metals

Cu, Pb, Cd, T-Hg, As, T-Cr, Al , etc.

Waste water

a. Main components

pH, EOD, COD, SS, n-Hex, Phenol, NH*, Cl~, CN~, etc.

Results of the experiment include descriptions of:

o Heat and material balance.

o Gas and energy recovery rate.

o Evaluation of the data from public nuisance standpoint.

o Cost estimation.

o Final economics.

From these results, the total process flowsheet for a commercial

plant, including pretreatment system was deduced. Thus, the final

output allows assessment of the commercial feasibility of the

paired fluidized bed pyrolysis unit under pilot plant conditions.

Key words: Baltimore County (MD) Resource Recovery Facility,

Cooperative Research ( Japan-U. S. ) , pilot plant scale-up for resource

recovery from waste destined for disposal, pyrolysis of refuse

derived fuel, refuse derived fuel gasification, solid waste management, waste-to-energy systems.

5.

8
Gasification of Refuse Derived Fuel in a

Paired Fluidized Bed Pyrulysis Unit

Report Completed

March 31, 1983

Received at NBS

April 11, 1983

Agency of Industrial Science and Technology,

Ministry of International Trade and Industry,

Government of Japan

In cooperation with Ebara Corporation, Japan

This work described in this report and the gasification

experiment were carried out in response to the—Tentative Agreement

for Joint Research Japan-United States, December, 1981.
CONTENTS

Page

1. Background 11

2. Introduction 11

(1) Outline of Stardust '80 11

(2) Process flow of pyrolysis system 12

(3) Experiment 13

(4) Schedule 14

(5) Operating conditions 14

3. Experimental results 14

(1) Properties of products and residues 14

(2) Mass and heat balances 20

(3) Utilities 20

4. Implications of Scale-up to commercial plant size 22

(1) Process and scale 22

(2) Predicted gas and energy recovery rates 24

Appendix 1. Pretreatment Subsystem 26

Appendix 2. Selective Pulverizing Classifier 29

Figures 33-42

10
1. Background

The Agency of Industrial Science and Technology (AIST) in the

Japanese Ministry of International Trade and Industry (MITI) has

been a strong advocate of the National Resource Recovery System R&D

program since its inception in 1972. In 1978, as the final phase

of this program the pilot scale plant "Stardust '80" was constructed

in Yokohama. Since 1979, many demonstration operations including

several periods of long-term operation, mostly using municipal

solid wastes from Yokohama as input material, have been performed

successful ly.

The goal of the program was to develop and demonstrate resource

recovery methods and equipment which would represent best possible

technology for pollution control, safety and maintenance, which

would also allow for economically efficient recovery of resources. This goal has been largely achieved; the technology which has been

developed is now ready for commercialization.

Nevertheless, the location and profitable exploitation of

suitable markets for the recovered resources is the next challenge

which must be dealt with satisfactorily. The viability of a resource

recovery system is largely dependent upon market capacity and

selling price of the recovered resources. Thus, part two of the

tentative agreement for joint research, Japan--Uni ted States

(December, 1981) calls for the application of National Bureau of

Standards resource recovery marketing and planning models.

2. Introduction

(1) Outline of Stardust '80 Yokohama Plant

"Stardust '80 (Yokohama Plant) was operated in the

fiscal year 1979-1980 1 as a materials recovery prototype

system meant to recycle such useful resources as compost,

pulp, fuel gas and light-weight aggregates from municipal

refuse. (Material Recovery System -MRS- operation).

Since April, 1981, energy recovery systems have been in

operation—in both Yokohama and Tokyo--to recover methane

gas and fuel oil. (Energy Recovery System--ERS—operation).

Fact Summary for Two-Bed Pyrolysis Gasifier

of Stardust '80 Yokohama Plant:

Opening: May 1979

Principals: Agency of Industrial Science and

Technology MITI (Owner)

Designer and Operator: Ebara Corp.

Volume: Design and actual; 24,000 kg per day in three shifts

1 The fiscal year in Japan begins on April 1.

11
Technology: Pyrolizer, dust collector, heat exchanger, gas

refiner and waste water treatment plant.

Products: Fuel, gas, electricity and steam.

Cost: $3 Million (1978 basis).

(2) Process flow of pyrolysis system

The pyrolysis gasification system consists of a pyrolysis

reactor and combustion reactor. A fluidizing medium (sand) is

circulated between two towers; the system is designed to perform

pyrolysis and combustion separately, for which reason it is called

"Two-Bed Type Pyrolysis."

Figure 1 shows the process flow. The input stock material is

fed into the pyrolysis reactor, and the fuel gas generated by

pyrolysis reaction is sent into the gas holding chamber after

undergoing char-separating, heat-exchanging and gas cleaning

processes. A portion of the resulting gas is recycled to the

reactor for utilization as fluidizer gas.

Meanwhile, the char (carbonized substances) generated in the

reactor is sent together with the sand to the combustion reactor,

where air is blown in to aid combustion. The remaining char, which

accompanies the pyrolysis gas, is intercepted and separated by means of a two-stage cyclone. The material is also burned in the

combustion reactor, where its energy contribution is utilized as a source of heat. The resultant energy generated by combustion is

transferred to the sand, which is then recycled to the pyrolysis

reactor.

The pyrolysis gas passing through the heat exchanger is

cleansed of oil, precipitated carbon bearing particles and noxious

gases by means of a spray tower and a scrubber. The scrubbing

water is sent to the waste water treatment unit where, after removal

of harmful substances, it is discharged into the local sewer system.

All of these operations are controlled by means of a centralized

system.

The exhaust gas generated by the combustion reactor is discharged into the atmosphere after being treated by means of a two-stage cyclone and an electrostatic precipitator. The non- combustible substances contained in the input stock material are discharged from the bottom of the combustion reactor periodically.

Features of Main Equipment Components

(i) Stock Material Feeder

The RDF is sent to the input stock material feeder (screw

type) from the storage silo by means of a constant rate feed

mechanism: the stock material feeder is of the solid-overflow type

so that the stock material usually can be kept at a constant level.

No bridging problems have been encountered to date with this

system.

12
The feeder unit has two-stages with a taper-type feeder

followed by a straight-type feeder which prevents gas leakage and

also prevents the stock material from being cracked at a low temperature. Therefore, even plastics, which previously were difficult to introduce properly, can be inserted very smoothly and at

a constant rate.

(ii) Reactor Body

The pyrolysis reactor and the combustion reactor are connected

by two pipes, which allows the fluidizer sand to circulate between

the two reactors. The temperature of the fluidizer sand, which has

undergone some reduction due to the endothermic thermal cracking

reaction occuring in the pyrolysis reactor, is sent to the sand

ejector together with whatever char is simultaneously formed. This

char reacts with the air stream introduced to blow the sand up to

the combustion reactor for burning; thus, the temperature of the

sand is raised. This hot sand is circulated back into the

pyrolysis reactor.

The sand circulation rate can be controlled satisfactorily by

merely injecting a small amount of air into the ejector section.

During operation, sand circulation rates ranging from 20 to 30

tonnes per hour have been maintained. In addition, the difference

in temperature between the upper and lower parts of the fluidized

bed can be stabilized to within ±2 °C, thus providing for a very

stable thermal field. The resultant pyrolysis gas has exhibited

high uniformity with few fluctuations in composition.

Incombusti bl es in the input stock material can be easily

separated and discharged by means of the air classifier stream.

The small amount of sand which is discharged along with these

incombustibles can be reintroduced into the combustion reactor

after the separation is accomplished.

(3) Experiment

An RDF gasification experiment was performed under the following conditions;

Place: Two-Bed Pyrolysis Gasification Subsystem

in Stardust '80, Yokohama Plant.

(Yokohama City, Kanagawa Prefecture)

Time: November 9-11, 1982

Stock

material: RDF (fluff) - 33.5 metric tons. Produced in Baltimore

County's Resource Recovery Facility, in Maryland, U.S.A.

This material was provided through the National Bureau

of Standards. The entire amount was disposed via

gasification during the above mentioned three-day period

13
(4) Schedule

On October 28, 1982, 33.5 tonnes of RDF were received and

placed in the storage pit of the Stardust 80 resource recovery

pilot plant. This RDF was confirmed to be in good condition (no

fermentation), despite the long transit time between the U.S. and

Japan.

A pyrolysis gasification experiment was carried out for three

days as follows:

November 8 Heat-up operation of reactor bodies

9-11 Pyrolysis gasification experiment

11 Blow-down operation

(5) Operating conditions

Table 1 lists important operating parameters for this experiment.

Table 1

RDF feed rate 700 - 1200 kg/hr <$4® -2,440 U„

a \\?A -• Pyrolysis reaction temperature 640 - 680 °C

Combustion reactor temperature 700 - 740 °C

Both reactors maximum pressure 600 - 1000 mmAq-gauge t% .(^- "i^ A; '*

Fluidizer sand circulation rate 25 - 30 tonnes 1 hr

This range has been found to include the most suitable temperature

for recovering energy from refuse.

Experimental Results

(1) Properties of products and residues

(a) Pyrolysis product gas

Table 3 lists the concentration of the pyrolysis gas recovered

in this experiment, and figure 2 shows the relation between pyrolysis

reaction temperature and gas composition produced from RDF.

The maximum calorific value of the pyrolysis gas from the U.S.

RDF was equal to the that of the gas produced by the MSW of

Yokohama City. Pyrolysis gas yield is about 0.5 Nm3 /kg-dry RDF in

the temperature range 650 °C to 670 °C; higher temeratures yield

more H 2 , CO and CH4 rich gas and less C02 rich gas.

The pyrolysis gas contains several potentially harmful gases.

Table 4 shows the concentrations of such gases before and after

scrubbing of the pyrolysis gas. These potentially harmful gases

14
can be minimized by alkali cleaning and water cleaning. The

product gas can then be used in power plants and other industrial

applications where medium BTU clean fuel gas would be economically

advantageous.

(b) Exhaust gas

Table 5 lists the components and concentrations of the com- bustion reactor exhaust gas along with the values specified as standards for incinerator exhaust gas in Japan. The concentrations

of the potentially harmful gases without gas cleaning and without

additives for the elimination of HC1 are lower than the incinerator

exhaust standard values. Moreover, the results confirm that the

present system contains intrinsic low-NOx-producing capabilities.

This capability occurs, in our view, because the temperature of the

combustion reactor is lower than that of conventional incinceration

systems.

Therefore, water was added to the RDF in order to increase its

bulk density, and the RDF moisture content was thus raised to 35%.

With regard to HC1 gas concentration, satisfactorily low

levels were maintained without adding the HC1 gas absorbent Ca(0H) 2

. Amounts of heavy metals are also satisfactorily low. Most of the

heavy metals in the RDF reported to the ash.

(c) Ash

Tables 6 and 7 respectively list the ash components and extraction procedure test results for the ash collected by the cyclone

and the electrostatic precipitator. Since the content of heavy

metals in the Baltimore County RDF is low, most of the heavy metals

reported to the ash. Each of the heavy metal values as determined

in this experiment satisfies Japanese Government mandatory requirements.

The ash ignition loss in weight is 1.9%; no unburned residue

could be found in the incombustibles discharged from both reactors.

(b) Waste Water

Table 8 lists the properties of raw and treated waste water

resulting from this experiment. The waste water treatment system

employs various physical-chemical treatments such as oil/water

separation, solid/liquid separation, stripping, filtration,

activated carbon adsorption, etc. The raw waste water has some organic contaminants (see BOD and COD) that exceed 1 percent, but

the concentrations of the heavy metals fully satisfy the standards

for Japan even in the raw waste water.

As a result, the treated water easily satisfies the requirements

set forth in the Kanagawa Prefecture Sewage Ordinance. This water

was therefore discharged to the local sewer system.

15
Table 2 lists the composition of the RDF provided for use in this experiment

Table 2. Composition of RDF

RDF

Moisture content % 14 ~ 20

Bulk density t/m3 0.07 * 0.09

Calorific value Kcal/Kg 4650 (gross); 8370 BTU/lb

3690 (net); 6640 BTU/lb

C 38.6%

H 5.7%

Ultimate 0 44.7%

analysis N 0.8%

S 0.17%

CI 0.23%

Ash 9.8%

Paper 66.7%

Textile 21.3%

Plastics 9.3%

Composition Yard waste 2.2%

Metals 0.5%

Glass 0%

Garbage 0%

a An inclined vibration conveyor, which is incorporated in the refuse

transfer line which was intended to carry the RDF from the storage

pit to the gasification site refuse silo, could not be used to

transfer the RDF (bulk density: 80hg/m3

) because this conveyor is

designed to deal with much heavier refuse (bulk density: around

250hg/m3

).

16
Table 3. Properties of pyrolysis product gas

Component

H2

N2

CH4

CO

C02

C2 H4

C 2 H6

C3

- Hydrocarbons

C4

- Hydrocarbons

Calorific

val ue

kcal

Nm3

concentration (%)

15.3 ~ 16.2

1.9 ~ 3.9

12.9 ~ 16.2

32.0 ~ 34.6

17.5 -v. 22.9

4.5 ~ 6.0

2.8 ~ 3.0

3.3 <v 3.7

1.3 «^ 2.0

* 5450 ~ 5850 (gross)

5020-^5400 (net)

* 610—655 Btu/ft3 ** 560—605 Btu/ft3

Table 4. Potentially harmful gas phase constituents in product gas

Components

H2 S

SO

x HCN

NH3

HC1

NO

Before After

scrubbi ng scrubbi ng

520 150

230 <10

711 14

142 <10

790 16

Not detected Not detected

unit: ppm

17
Table 5. Properties of exhaust gas

Incinerator

Concent- exhaust

ration standard value

7. 5%

Main gas N

2 81.4%

CO2 11.13

HC1 152 ppm <430

Harmful NOx 76 ppm <250

gas SOx <10 ppm <300a

Soot dust 0.06 g/Nm-3 <0.1

Ld <0. 01 mg/Nm°

Heavy Metal

s

ex.c. ru U. i/ mg/Nm0 <10

b

LU u. lb mg/Nm°

T-Cr 0.02 mg/Nm3

T-Hg <0.01 mg/Nm3

As <0.01 mg/Nm3 a Stipulated K value (K = 1.17).

General smoke emission standard values.

Table 6. Ash components

Concent- Concent- ConcentComponents ration (%) Components ration (%) Components ration (ppm)

C 1.1 Na 2.3 LU o/in

H <0.3 K 1.1 Pb 84

N <0.3 Ca 0.32 Cd 6

S <0.03 Al 5.9 T-Hg 0.01

CI 0.28 Ignition T-Cr 120

loss in 1.9

weight As 2.9

18
Table 7. Extraction procedure test value of ash

Concent- Standard

rat inn wal lip

Cd <0. 01 <0 3

PhrU

Asi

1 4 3> <0 05 <1 5

Cr6+

<0. 05 <1 5

T-Ha <0 0005 <0 005

R-Ha a \ o b Not detected Not riptprtpri

Ora-P <0. 01 <1

<0 0005 <0 003

CN- <0.

1

<1

unit: mg/1

Standard values for landf i 11 ing in Japan.

Table 8. Properties of raw and treated waste water

Raw Treated Standard

waste water waste water val ue PH 8.0 7.3 5.7 -v BOD [mg/£] 18,000 50 <300

COD 14,000 90

Suspended Solids 690 19 <300

Phenols 11 1,100 <0.05 <0.5

Cd 0.03 <0.01 <0.1

CN- 20 <0.1 <1

Pb 0.1 <0.1 <1

T-Hg 0.0006 0.0005 <0.005

Cu <0.1 <0.1 <1

T-Cr " <0.05 <0.05 <2

n-Hexane " 230 <5 <5

340 136

CI 1,200 900

Requirements set forth in Kanagawa Prefecture Sewage Ordinance.

19
(2) Mass and heat balances

Figures 3 and 4 illustrate the mass and heat balance relationships

obtained in this experiment. As shown in figure 3, 317 Nm of medium

BTU fuel gas was produced from 1139 kg (moisture content 35 percent)

of RDF in one hour. The gross calorific value ranges from 5450

5850 Kcal/Nm3 in the pyrolysis reaction temperature range of 640 *

680 °C. The experimental results indicated that 191 Nm3 fuel gas

and 280 kg (6 kgf/m2

) steam could be recovered as products which

could in turn be supplied to some external location.

Details concerning mass and heat balance can be outlines as follows:

Gasification rate 1 51.3 % (Kcal-gas/Kcal-RDF)

Gas energy recovery rate 30.5 % (Kcal-gas/Kcal-RDF)

Total energy recovery rate 2 36.2 % (Kcal-gas. steam/Kcal-RDF)

* Gasification rate = calories of dry product gas

calories of dry RDF

total recovered calories

2 t *. i * of gas and steam * Total energy recovery rate = t ;—: , nr>r

. *J J total colories of RDF

Experimental factors affecting the observed energy recovery

include the following as there were virtually no i ncombustibles in

the RDF:

(i) operations meant to separate and discharge the i ncombustibles

from the pyrolysis reactor were not necessary and

(ii) discharging the high temperature fluidizer sand (including

some i ncombustibl es) from the combustion reactor was also

unnecessary. Therefore, typical input energy requirements

for the reactor were reduced and a significant amount of

auxiliary fuel gas (product gas) was thereby saved.

To correct the results of the energy recovery rate computed

for typical input RDF with a 15 percent moisture content (as

mentioned before, moisture was increased to around 35 percent by

the need to add water to the RDF) we used the following values:

Gas energy recovery rate 38.1 percent (Kcal-gas/Kcal-RDF); Total

energy recovery rate 43.8 percent (Kcal-gas. steam/Kcal-RDF).

(3) Utilities

Table 9 lists the operating costs of this gasification experiment.

Since the pilot plant was designed for the purpose of research

and development with respect to gasification technology:

1. Some equipment in the system, such as compressors and blowers,

has built-in excess capacity meant to cope with unusual

experimental conditions, e.g., aimed at the determination of

the upper limits of the system's operational capabilities.

20

1
2. In the waste water treatment system, physical-chemical treatment

facilities had to be employed instead of less costly biological

methods because of the long shutdown intervals occasioned by the

irregular testing schedule for Stardust 80. (With biological

treatment systems, it is difficult to maintain the function

properly while the system is not in operation).

The right hand column of table 9 therefore shows our estimate of operating

costs corrected to conform to optimal conditions.

Table 9. Utilities and operating costs

Consumption Cost in yen Corrected cost

per hour per refuse ton in yen per refuse ton

Electricity 340 kWH 5,236 2,510

a

Water 4 m

3 1,080 1,080

Town gas

b

2 Nm3 316 316

Nitrogen gas 0.7Nm3 210 210

Sand 15 kg 150 150

Chemicals

for boiler 1 kg 800 800

25 % NaOH 9.4 kg 348 348

35 % H

z S04 6.5 kg 410 410

1 % coagulant 6.1 kg 134 134

Activated carbon 30 kg 9,750 270

C

Ca(0H)

z

0 kg

Nouri shi ng

salinity 0 kg 20

Total 18,434 6,348

a Since 52% of the electricity can be generated by a gas engine (see

description below) using recovered fuel gas, the purchase of only

163 kwh of electricity is needed.

k

Town gas is used for the pilot flame of the auxiliary burner.

r With the physical—chemical treatment large amounts of activated

carbon are consumed, but in the case of the biological treatemnt,

almost all of them are saved.

21
Gas engine generator

Since 1980, the gas engine generator has been operated for

more than 1,000 hours using over 70,000 Nm3 of recovered fuel gas.

We have confirmed that the gas recovered was sufficiently clean and

high in calorific value' to use for the gas engine, and that the

efficiency of energy conversion was as high as 35%. The gas

engine employed in the Stardust '80 Plant is a slightly modified

standard diesel engine, the main specifications for this engine are

as follows:

Type 4 cycle, water cooled, vertical type

Cylinders 6—150 X 165

Generating power 300/1800 PS/RPM

200 kw

4. Implications of scale-up to commercial plant size

(1) Process and scale

In this section, computations describing the expected characteristics of a commercial-scale plant based on the Stardust '80

resource recovery system are discussed.

Calculations for the following two cases were performed by

means of a modified computer program which was developed on the

basis of the previously described gasification experiment.

Case 1: Pyrolysis gasification plant (including gas engine

generator) stock material: RDF 1000 tonnes/day (produced

in the U.S.). In this case, RDF is gasified with the

same process as that of the Stardust '80 Plant.

Case 2: Pyrolysis gasification plant (including pre-treatment

system and gas engine generator) stock material:

Municipal Solid Wastes from the U.S.: 100 tonnes/day.

Fig. 5 shows the schematic process flow of case 2.

In both cases, required electric power is assumed to be

supplied by a gas engine generator fed by product gas from the

gasification process.

In both cases, all the raw waste water coming from the product

gas refiners is assumed to be burned in the combustion tower.

MSW is separated into two parts (group A and B) by a selective

pulverizing classifier, see Appendix 2). After the ferrous metal

is removed, group B is shredded to a size less than 150 mm and fed

to the reactor, where it is gasified. A fraction of the product

gas is consumed by the gas engine generator to meet all demands for

electricity in the plant.

22
The material in group A is assumed to be discharged as residues to be

landfilled together with the i ncombusti bl es (glass, metals, etc.) discharged

from both reactors.

Table 10 lists the results of separation of U.S. municipal refuse

predicted by the SPC simulation model. This model was developed on the basis

of the results of the processing of over 20,000 tonnes of Japanese MSW taken

from various sources. The calorific value of the group B refuse is calculated as 4,600 Kcal/kg-dry (gross) or about 8300 BTU per pound.

Table 10. Results of separation of U.S. municipal refuse predicted

by Selective Pulverizing Classifier simulation model

Input refuse

3

Group A Group B

Paper 42.7 28.1 51.7

Glass 11.1 47.0 3.1

Metal 11.1 1.1 3.0

Plastics 9.9 0.7 13.5

Rubber 3.3 0 4.5

Textile 5.9 0.1 8.1

Wood 11.9 8.6 14.2

Garbage 3.5 13.6 1.3

Others 0.6 0.8 0.6

Total 100 100 100

Fraction 100 18.8 72. 9

b

Moi sture 19.0 24.2 19.4

unit: %

a Municipal solid waste of Baltimore County Md.

k The remaining 8.3% is recovered as ferrous metal by magnetic

separators.

23
(2) Predicted gas and energy recovery rates

Figures 6-9 show the mass and heat balances applicable to case

1 and case 2, respectively. The efficiency of the plant for each

case was computed to be:

Case 1 Case 2

Gasification rate 52.8 % 47.1 %

Gas energy recovery 43.6 % 35.1 %

rate

Total energy recovery 57.1 % 40.5 %

rate

Tables 11-13 list the results of the calculations applicable

to required utilities, recovered materials, site area, personnel

and capital costs.

Table 11 Utility Requirements

Case 1 Case 2

City water (t/d) 969 560

Industrial water (t/d) 1790 1620

Chemicals (Ca(OH) 2

) (t/d) 5.3 8.3

Sand

3 (t/d) 4.8 7.4

a Average particle size is 0.56 mm.

Table 12. Recovered materials

Case 1 Case 2

Fuel gas

3 (Nm3 /d) 305 x 10 3 172 x

Steam

b (t/d) 811 407

Ferrous metal (t/d) 0 70.5

3 Calorific value of product gas

Case 1: 5650 kcal/Nm3 (630 Btu/ft3

) Case 2: 5500 kcal/Nm3 (620 Btu/ft3

)

Steam pressure: 16 kgf/cm2

These volumes of fuel gas and steam are those predicted to be

recovered after all other plant energy demands (including electricity)

have been taken into account.

24

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25
Appendix 1

Pretreatment Subsystem

The pretreatment subsystem handles such operations as the

weighing, receiving, storing and classifing of the collected refuse

mixture so as to supply each backend subsystem with stock material.

The main equipment in the pretreatment subsystem is the selective

pulverizing classifier (SPC).

The classifier has a circular shape and is approximately 3

meters in diameter and about 8 meters in length. The input refuse

mixture, delivered by conveyor is fed into the classifier, where

the refuse is classified via passing through a trommel. The

classified refuse is dropped out onto other conveyor belts provided

below the classifier and carried to each subsequent subsystem.

This equipment comprises a cylindrical rotary screen drum and a pulverizing scraper plate. The latter is incorporated into the

former but rotates at a speed different from that of the rotary

screen drum. Thus, the refuse is pulverized and classified

simultaneously.

The first items of input refuse to be pulverized and

classified with the rotary screen drum are garbage, soil and sand

and glass and chinaware, all of which are relatively brittle; the

refuse so classified is referred to as Group I material. The

remainder of the refuse passes through the screen drum; water is

sprayed onto the refuse at the center of the pulverizing scraper

plate in the second screen drum. This water is absorbed by paper

and other materials in the refuse. The resulting mixture has lower

impact resistance and shearing force than the dry material. Thus,

the mixture can easily be pulverized on the pulverizing scraper

plate and selectively discharged from the second rotary screen

drum. The material so discharged is referred to as Group II. The

remaining refuse consists of plastics, metal cans, etc., which are highly resistant to impacts and shearing forces.

This material is referred to as Group III and is discharged at

the furthermost end of the drum. Table "a" lists the refuse com- ponents as classified by means of the selective pulverizing

cl assi f ier.

26
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27
The pretreatment subsystem includes the following features:

(a) Capable of simultaneously pulverizing and classifying

refuse in a single process and with a low rate of power

consumption.

(b) Group I is composed mainly of garbage, which may be used

for compost.

(c) Group II is composed mainly of paper, which may be used

for pulp.

(d) Group III is composed mainly of plastics, and is thus a favorable feedstock for gasification.

(e) In response to changes in input refuse composition or in

requirements for classification, the pretreatment subsystem

permits easy alteration of the degree of classification.

This control is achieved by changing the feedrate of

refuse in the drum and/or the relative velocity of both

the pulverizing scraper plate and the drum.

28
Appendix 2

Selective Pulverizing Classifier (SPC2)

1. Functions

(1) Separation capability: SPC2 can classify municipal

refuse into two groups, i.e., compostable materials and

non-compostable materials.

(2) Crusher: SPC2 can crush compostable materials in municipal

refuse into sizes suitable for aerobic fermentation.

Excessive crushing is avoided, because it not only wastes

power, but may also rupture dry batteries in the waste

could cause heavy metal contamination in the compost.

(3) Bag-breaker: SPC2 can cope with refuse collected in

plastic bags or boxes.

2. Features.

(1) SPC2 can be used directly to apply suitable moisture for

aerobic fermentation.

(2) SPC2 tends to operate properly even if bulky items such

as metal appliances are charged.

(3) Entanglement of long strings around the rotary shaft, a major problem with conventional shredders, is said to be

eliminated by the wrap prevention device specifically

developed for this machine. This feature renders the

manual removal of strings unnecessary and greatly reduces

maintenance time.

(4) Unlike conventional trommel type screens, this sieve is

unlikely to become clogged because of cleansing function,

of scrapers.

(5) Because of its very low speed, this classifier creates

far less wear, noise and vibration than conventional

high-speed shredders. The SPC2 which incorporates both

pulverizing and classification by screening in one machine,

developed with full support of the Agency of Industrial

Science and Technology (AIST of MITI of Japanese government)

and was awarded the Directors Prize of the Ministry of

Science and Technology in 1977, and the Mechanical Institute

Prize in Japan 1978.

3. Brief description of equipment

(1) General. Pretreatment for composting refuse requires

three basic functions: 1) elimination of non-compostable

materials, 2) size reduction without operating leakage

from dry batteries, and 3) moisture adjustment.

29
1) The elimination of non-compostabl e materials such as plastics, metals, textiles, etc., from raw refuse

before fermentation yields the following important

advantages:

a) The capacity of the fermenter can be increased

substantially by the elimination of non-compostables

,

particularly plastic films and the like, which

have a large specific volume.

b) Heavy metals contained in the non-compostables

may dissolve into the compost during the course

of the preliminary fermentation, thus lowering

the pH value of the final product.

c) Bulky textiles and long strings contained in

the refuse often become entangled in the stirring

mechanism of the usual type of fermenter.

2) Size reduction to obtain a large specific surface of

the material is preferable for fast fermentation.

Excessive pulverization, however, must be avoided,

since it not only requires a large amount of power

but also ruptures dry batteries leakage from which

may cause heavy metal contamination in the compost.

3) The moisture of the pretreated compostable material

must generally be kept within a limited range (about

40 to 60% depending on the type of fermenter) which

is suitable for aerobic fermentation.

(2) The Selective Pulverizing Classifier (SPC2): Based on the preceding three requirements, the SPC2 (Selective

Pulverizing Classifier) was developed. The SPC2 takes

advantage of differences in the resistance to destruction

of different material; both pulverization and classification by screening can be accomplished with the aid of

this one machine. As shown in appendix figure 1, the SPC2

consists of a rotating drum screen and a scraper rotating

at a different speed inside the screen.

As the refuse is fed continuously into the rotation drum,

almost all of the garbage (food waste) and brittle materials such

as dirt, glass and ceramics, and a fraction of the (flimsy) paper

are pulverized into particles or flakes and pass through the screen

(A Group). The remaining residues consisting of plastics, metals

and textiles etc., are discharged through the open end of the drum

(B Group).

In the case of dry refuse input, moisture can be increased by

spraying water from a tap built into the central shaft so that the

optimum water content for fermentation of A Group material can be

easily obtained. Additional moisture can also increase the paper

concentration in A Group owing to the resultant strength reduction

of the paper.

30
In the case of wet input (considerable amounts of wet garbage),

an increase in the relative speed between the drum and scraper

produces a considerable increase in the pulverizing effect and in

the concentration of dry paper in A Group which in turn decreases

its total moisture content.

Unlike the conventional shredder, which completely shreds all

the refuse, this classifier discharges B Group materials from the

drum end following the process of selective pulverization. This

refuse remains close to its orginal size. Almost all of the dry

batteries contained in the refuse maintain their original shape and

remain sealed.

Small batteries are discharged into the A Group without being

shredded. These batteries are separated by the magnetic separator.

The size of pieces of glass and ceramics discharged into A Group is

extremely large compared with that produced by conventional shredding.

These remnants can be easily removed after fermentation.

4. Engineering Aspects.

SPC2 consists of a rotating drum screen equipped with ridge

projections, rotating scrapers inside the drum screen, and a drive

unit which drives both the drum screen and the rotating scraper by means of one motor protected by a safety device.

The motion of the rotating drum screen is controlled by means

of a chain driven by the motor followed by a reduction gear. The

RPM value is kept constant within the range of 20 to 40 rpm.

The rotating scraper located inside the rotating drum screen,

is controlled by means of a belt driven by the SPC2's single motor

and a infinitely variable transmission. The RPM of the rotating

scraper is variable within the range of 40 to 80 rpm.

The rotational direction of the scraper is the same as that of

the drum screen, but the rotational speed is different. Therefore,

shear stress arises and pulverization occurs in the region between

the scraper and the ridge projection mounted in the inside of the

drum screen.

5. Separation Performance

Table "b" lists test results for separating a sample of

municipal refuse with the SPC2. As seen in this table, garbage

(kitchen refuse) was concentrated by a factor of about two, and

plastics and textiles, the main components of RDF, were almost

completely discharged through the open end of the drum as B Group.

Accordingly, the SPC2 was judged to be suitable separating

equipment for the plant producing both RDF and compost from municipal

refuse. Since the particle diameter of the compostable materials

(A Group) from SPC2 is pulverized and homogenized to a size of

about 20 to 40 mm, extremely good fermentation can be achieved.

31
6. Utility Requirement.

Electricity consumption of the SPC2 is 10 to 15kwh/tonne

(input refuse).

Table b. Test Result of SPC2

Municipal

Refuse A Group B Group

Composition

(%)

Composition

(%)

Classification (%)

Composition

(%)

Classification (%)

Paper 56.3 58.1 49.1 55.0 50.9

Garbage 14.5 29.4 96.6 1.0 3.4

Texti le LO.O 0.6 3.6 18.5 97.0

Wood 2.6 1.7 31.0 3.4 69.0

Dirt 0.8 1. 7 100. 0 0.0

Glass 3.3 6.9 100.0 0.0

Metal 8.2 0.8 5.0 14.9 95.0

Plastics 4.3 0.8 10.0 7.2 90.0

Total (Dry) 100.0 100.0 100.0 100.0

Moi sture

(Content) (%) 49.3 54.5 40.2

a Each rate of classification described in this table assumes that

sewage sludge is not mixed with refuse. Mixing refuse and sludge

causes an increase of classification rate of paper in the A Group.

32
33

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35

MSW

SPC

electricity

Group A

MG CR TPS

Ferrous

metal

Steam

GE

Fuel gas

SPC

MG

CR

TPS'

GE

— 1 > Residues

Selective Pulverizing Classifier

Magnetic Separater

Crusher

Two-bed Pyrolysis syst

Gas Engine Generator

; em

Figure XIII. 5. Schematic process flow.

37
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41
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Appendix Figure 1.

42
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

PUBLICATION OR

REPORT NO.

NBS SP 664

2. Performing Organ. Report No 3. Publication Date

September 1983

4. TITLE AND SUBTITLE

Gasification of Refuse Derived Fuel in a Paired Fluidized Bed Pyrolysis Unit

5. AUTHOR(S) s> Suzuki (Gov't of Japan)

Harvey Yakowitz (NBS)

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

(Results developed as part of the scientific exchange program of the respective

governments of Japan and the United States)

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 83-600583

J Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT ( A 200-word or less factual summary of most significant information. If document includes a significant

bi bliography or literature survey, mention it here) As part of the scientific interchange program initiated by the United States

Government and the Government of Japan, the Department of Commerce was selected by the

White House to be the pilot agency for a project concerned with resource recovery from

discards originally destined for waste. Such discards include municipal waste and

industrial waste. Under terms of the agreement signed by the President and the Prime

Minister on May 2, 1980, the United States and Japan will exchange small teams of

government scientists in order to examine resource recovery in the respective countries

and to formulate possible joint research ventures.

The Office of Recycled Materials of the National Bureau of Standards (NBS/ORM)

,

which was charged with fulfilling the duties assigned to the Secretary of Commerce by

Subtitle E of the Resource Conservation and Recovery Act as amended (P.L. 94-580;

PL 96-482) was designated as the U.S. contact point for this project. The Japanese team

visited the U.S. in December, 1981; NBS/ORM arranged the itinerary and provided

technical briefings and an overview of resource recovery activities. At that time,

NBS/ORM and Japanese representatives concluded an agreement for joint research to be

performed as part of the project. The results described in this report were developed in partial fulfillment of this agreement.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Baltimore County (MD) Resource Recovery Facility* Cooperative Research ( Japan-U . S . )

,* pilot plant scale-up for resource recovery from waste destined for disposal,*

pyrolysis of refuse derived fuel; refuse derived fuel gasification,* solid waste managemeji

13. AVAILABILITY

[XXUnlimited

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14. NO. OF

PRINTED PAGES

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